I think it is the best single player ARGP. It has the old school vibes of D2 and TQ and the modern features of say Diablo 3 with quick and fluid combat, and the advanced and game mechanics and build diversity of PoE. I have a very old series where I compare and explain D2 vs Grim Dawn
Now, there are two more expansions (one of which will be released next year)
There are two things that I do not like about Grim Dawn
1) Loot is almost too easy to get. Except a few items. Not as easy as in Diablo 3 - but there is still no "grail" feeling sort of.
2) Patching destroys too many builds. The devs are imo too extreme when it comes to balancing and tweaking the game. And quite often certain builds just gets killed by patch. I think this would make sense if it was a ladder/season based game but not for a single player offline ARPG. Sure, in the GD community we love that there are soo much build diversity and extremely good balance. But the devs still wanna tweak tweak tweak... like I took a two year break from the game, only a handful of my builds where "playable" when I went back - this is a bit detrimental imo
EDIT: two more things I dislike
Slow run speed, there is a cap on run speed which is kinda weird. Speed is king
Class identity, since there are like 50 different classes - they are hard to distinguish both skill wise and lore wise. It is more of a spectrum than discrete black/white...
